1. Field of the Invention
This invention relates to a terminal for a connector used mainly for connecting wire harnesses in automobiles, and the invention also relates to a method of producing such a connector terminal.
2. Related Art
FIG. 8 shows the structure of one conventional connector terminal.
A receptive portion 2 and a spring portion 3 for a mating terminal are provided at a front portion of the terminal 1. The receptive portion is defined by a base plate 4, opposite side walls 5, and a top wall 6 which is formed by bending free end portions of the side walls 5 into overlapping relation to each other above the base plate 4. The spring portion 3 is formed by folding back the base plate 4 at the front end of the receptive portion 2, and is received in the receptive portion 2.
Conductor clamping portions 8 for electrical connection to a wire by compressive clamping or soldering, as well as insulator clamping portions 9 for mechanically gripping an insulative covering of the wire, are provided at a rear end portion of the terminal 1.
Such terminals are manufactured by sequential processing, using a pressing machine (not shown). Referring to FIG. 9, in the sequential processing, many steps including blanking and press-shaping are incorporated in a set of upper and lower press dies, and a blank 10 in the form of a thin metal sheet is sequentially fed step by step between the dies, and at a final stage of the process, a shaped product is discharged. Thus the blank 10 is processed into terminals 1, having a configuration shown in FIG. 8, merely by passing the blank 10 through the single pressing machine.
If the size of the terminal is made smaller in order to meet a demand in the market for a compact design of the terminal, the allowable maximum deflection of the spring portion 3 is smaller, and particularly when such a terminal is used in an automobile, there arises a serious problem in that durability, such as vibration resistance, is adversely affected.
Expressing this problem in terms of formulas, if the spring portion 3 is regarded as a cantilever beam of a concentrated load-type in FIG. 10, and if L represents the length of the beam, t represents a wall thickness, W represents the width of the spring portion 3, F represents a contact load of the terminal 1, E represents Young's modulus of a spring material, D represents the maximum deflection, and S represents the maximum stress, then known formulas (1) and (2) in connection with the strength of materials can be applied, and another formula (3) representing the maximum deflection D can be derived from the two formulas as follows: EQU D=12FL.sup.3 /3EWt.sup.3 ( 1) EQU S=6FL/ Wt.sup.2 ( 2) EQU D=2SL.sup.2 /3Et (3)
For increasing the allowable maximum deflection D in order to deal with the above problem, the following measures are suggested from the above formula (3):
1) To adopt such a configuration that the ratio of the dimension L to the overall size of the terminal is increased as much as possible. PA1 2) To choose such a material for the spring portion that the allowable maximum stress S is large. PA1 3) To reduce the thickness t of the spring portion.
To use a material with low Young's modulus is contrary to the intended purpose of the spring portion, and therefore this can not be adopted.
In one conventional method of increasing the effective length L of the spring (which is one of the above measures), a spring portion 3 has been formed into a coil spring-like configuration as shown in FIG. 11. In this method, however, the spring portion is complicated in structure, and also in order to stabilize the dimensional accuracy of the configuration, high precision techniques are required, which leads to a high manufacturing cost. A further drawback is that since a curved portion with a large radius is provided at the front end of the spring portion, the spring is susceptible to deformation due to prying by a tool.
With respect to a method of choosing a material with a large allowable maximum stress S, such a material is usually expensive, and if the whole of the terminal is formed of such a material, the manufacturing cost becomes high. If the whole of the terminal is formed of a material with a small thickness t, there is encountered a serious drawback in that the retaining strength to prevent rearward withdrawal of the terminal is decreased.
Therefore, there has heretofore been used a method in which a spring portion 3 is formed of a material different from that of the remainder of the terminal, or has a thickness different from that of the remainder, and the spring portion is formed in a separate process, and in a final step, the spring portion is mounted within a receptive portion 2 as shown in FIG. 13.
In the manufacture of such two-part terminal, however, different pressing machines as well as different press dies are required for pressing the spring portion 3 and the remainder, respectively, as shown in FIG. 12, and an assembling machine is further required. Therefore, the installation cost is increased, and the yield becomes low because of defective mounting of the spring portion.
In construction shown in FIG. 14, a connector terminal c, received in a terminal receiving chamber b of a connector housing a, is retained by an elastic retaining tongue d against rearward withdrawal. The connector terminal c includes a receptive portion e and a wire connecting portion f, and a retaining projection d.sub.1 of the cantilever-type elastic retaining tongue d engages a retaining portion e.sub.1 defined by a rear shoulder of the receptive portion e.
As shown on an enlarged scale in FIG. 15, the retaining portion e.sub.1 has an edge e.sub.1 ' formed by a cut surface of a thin metal sheet, and a large retaining area p (the distance between the edge e.sub.1 ' of the retaining portion e.sub.1 (i.e., the proximal contact end for the retaining projection d.sub.1) and the distal end of the retaining projection d.sub.1) can be provided, and a large part of a projection area q of the elastic retaining tongue d (the distance between the proximal end to the distal end of the retaining projection d.sub.1) can be utilized. However, there is a drawback that the sharp edge e.sub.1 ' damages the retaining projection d.sub.1.
In the construction shown in FIG. 16, a retaining portion e.sub.2 of the terminal c is made bending a sheet, thereby providing an arcuate corner portion e.sub.2 '. In this case, because of the edgeless arrangement, damage to the elastic retaining tongue d can be prevented; however, because of the provision of the arcuate corner portion e.sub.2 ', the retaining area p' of the retaining portion e.sub.2 for the retaining projection d.sub.1 is reduced, and in order to ensure a satisfactory retaining effect, it is necessary to increase the retaining projection d.sub.1 to increase a projection area q' as shown in phantom. However, the increased projection area leads to a disadvantage in that the overall size of the connector housing is increased.